It is known to shape the mouth of a chimney or smokestack or to provide the latter with a static device for increasing the draw of the chimney and for suppressing backflow of gases downwardly therethrough. Such devices are generally made from metal, ceramic, or concrete and are usually manufactured in a factory and transported in a finished state to the erection site at which they are placed upon the chimney.
While metal structures of this type are relatively simple to fabricate, they are highly sensitive to oxidation, particularly in the presence of sulfurous gases which are formed during combustion of the fuel. In practice, such devices are only installed by specialists, i.e. so-called chimney specialists, especially trained to mount the device on the chimney and to construct the device.
It has also been proposed to shape the mouthpiece of a chimney or smokestack in situ and, to this end, the construction of the mouth of the chimney may be carried out by masons during the erection of the chimney. However, such chimney-mouth configurations have been found to be less than satisfactory with respect to increasing the draw of the chimney and, because the device is fabricated in situ, it generally has poor aerodynamic qualities and does not provide optimum results with respect to combustion. Finally, in this regard, the in situ formation of the mouthpiece configuration requires skilled personnel, is time-consuming and is expensive.
It has also been proposed to provide draw-promoting devices which are fabricated from cement and are generally produced in factories or the like and transported to the site at considerable cost. Furthermore, these devices are highly fragile and, because they are heavy and difficult to manipulate, are prone to damage. Frequently, therefore, a unit of this type transported to the erection site is found to be defective because of some damage resulting from its fragile character and its weight. The device must be replaced, i.e. another unit must be shipped. This holds up erection of the factory or other structure provided with the chimney.